Several classes of hydraulic cements are known such as Portland cement, high-alumina cement, and gypsum which are categorized by their chemical composition and use. For example, Portland cement is commonly used in structural applications and is high in silicate content. In this disclosure the term "cement" shall refer to silicate cement compositions including Portland cement, pozzolanic cements, hydraulic limes, fly ash and natural cements. Cements are used in concrete, grouting and mortar compositions which contain other components such as sand and gravel, or stone.
Cement compositions are rendered useful by the combination of the solid components with water. To obtain a mixture with sufficient workability in order to pour into a mold or form, an amount of water in excess of that required for hydration of the cement components is necessary. During the hardening of the composition, the excess water remains and ultimately, as it evaporates, causes cavities to be formed in the hardened molded structure. These cavities reduce the integrity of the structure and result in a compressive strength which is lower than that theoretically obtainable. It is, therefore, desirable to use the lowest amount of water possible in a cement composition in order to obtain the best compressive strength. Since low amounts of water, while desired for strength, make workability difficult, a compromise is called for.
Additives which cause the strengthening of cement compositions by water reduction while allowing the mixtures to have adequate workability are commonly called water reducers or plasticizers. Those which allow high levels of water reduction are known as high range water reducers or superplasticizers. Application of such materials in cement compositions that have normal levels of water result in mixes with increased fluidity or workability. Lignin sulfonates and sugars are common plasticizers while typical commercial superplasticizers are sulfonated melamine-formaldehyde condensates or sulfonated naphthalene-formaldehyde condensates. In addition, sulfonates of styrene polymers have been described as fluidizing agents for cement compositions.
U.S. Pat. No. 4,164,426 teaches the use of zinc naphthalene-formaldehyde sulfonate in concrete mixes for improved compressive strength. The patented material claimed functions as a superplasticizer but with the added advantage of producing higher strength than normally obtainable, e.g. with the sodium salt of naphthalene-formaldehyde sulfonate.
U.S. Pat. No. 4,071,493 describes alkali metal salts of sulfonated styrene-indene hydrocarbon resins as fluidizing agents for mineral binders.
British Patent No. 1,588,130 describes a hydraulic cement composition which includes a plasticizer comprising a sulfonated polystyrene. It is taught that the sulfonate is preferably used in the salt form. The inclusion of a water soluble carbonate in the composition apparently improves the plasticizing effect of the sulfonated polystyrene although the sulfonated polystyrene may be used with or without the carbonate.
U.S. Pat. No. 4,076,699 describes a process for the preparation and use of alkali salts of a sulfonated styrene polymer or copolymer as fluidizing agents for mineral binders.
The materials exemplified in the patent are the sodium and potassium salts of sulfonated polystyrene and the sodium salt of sulfonated polyvinyltoluene. While it is taught that any styrene or substituted styrene monomer may be copolymerized to yield the fluidizing products of the invention, no examples of such copolymers are given.